The present invention relates to a transparent, hard, laminated or layered packet comprising at least one coating of TMDS (tetramethyldisiloxane) and a top coating of TMDS hardened by oxidation. Furthermore, the present invention relates to a method for producing such a layered system on a plastic substrate in which the substrate is first coated with TMDS (tetramethyldisiloxane) and then a top coating of TMDS hardened by oxidation is applied thereupon.
Plastic substrates must frequently be provided with a transparent coating as protection against scratching and wear. This is the case, for example, with eyeglasses made of plastic because they would be scratched without such protection against scratching if a hard grain of dust would be on the eyeglasses when being cleaned with a cloth. Protection against scratching is also desirable on protective glasses for the lenses of motor-vehicle headlights, especially when the protective lenses are cleaned by wipers. A coating of protection against scratches is also desirable for compact disks and displays.
Up to the present, eyeglasses were first provided with a soft coating of TMDS and then with a coating of TMDS, oxidized during deposition in the plasma by pure oxygen and hardened as a result of the oxidation reaction. However, such a laminated system does not meet the current, very stringent requirements placed on eyeglasses. Such coatings are often destroyed, especially in the boiling test, because not all OH groups can be removed in the TMDS by the oxygen or, alternatively, they re-form. Even the other tests customary for eyeglasses, for example, the scratch test with a rubber eraser, the tumble test in a rotating drum with various added materials, the impact test and the temperature test only yield unsatisfactory results in the case of the known coating systems. That also applies to plastic glasses with vaporized-on quartz and to plastic glasses with coatings applied by wet chemical processes.
Therefore, an object of the present invention is to meet the high requirements placed on coatings for eyeglasses with a coating system having as high a transparency as possible in the optically visible spectrum and in the range close to the UV.
It is a further object of the present invention to provide, a method of producing such a laminated coating system.
The above and other objects of the invention can be achieved with several coating sequences comprising in each instance TMDS and hardened TMDS superposed over each other and by locating a thin, transparent separating coating of carbon between each such coating sequence.
Such separating coatings, which can be so thin that the transparency of the coating system does not suffer, can be used to produce a relatively thick coating system consisting of several coinciding coating sequences which system has a high degree of flexibility in spite of great hardness because the columnar growth in the TMDS coatings is interrupted by this separating coating. As a result of the non-hardened TMDS coatings the ball impact test, for example, can be reliably passed without peeling or chipping off occurring.
The substrate is especially well protected against scratching if the layered coating system comprises a non-hardened coating of TMDS on the outer side and a transparent cover coating of carbon applied onto it. The carbon coating adheres on the unhardened TMDS much better than on hardened TMDS so that a peeling off need not be feared.
In the case of plastic eyeglasses the optimal dimensioning of the coating system was found to be when the TMDS coating is approximately 1 xcexcm, the hardened coating of TMDS approximately 0.2 xcexcm, the separating coating approximately 3-5 nm and the cover coating approximately 10-15 nm thick.
The creation of a layered coating system on a plastic substrate, is achieved in accordance with the invention in that at least another, coinciding coating sequence is applied onto the coating sequence of TMDS and hardened TMDS and that a separating coating of carbon is formed between each coating sequence.
Such a laminated packet can be applied, e.g., by means of an RF plasma reactor. An average RF power output is used for the soft TMDS coatings whereas for the hardened TMDS coatings and the separating coatings a high RF power is required. All plasma processes operate at pressures between 0.1 to 20xc3x9710xe2x88x923 mbar. The layered coating system of the invention meets all currently customary tests for plastic eyeglasses and is distinguished in particular by great scratch resistance and hardness with great elasticity at the same time and, as a result, security against delamination.
According to an advantageous further aspect of the method of this invention, the layered coating is provided on the outside with a non-hardened coating of TMDS and with a transparent cover coating of carbon applied onto it. Such a cover coating increases the scratch resistance even more without any danger of peeling off.
The carbon for producing the separating coating and the cover coating can be deposited especially well for forming xcex1 carbon if the deposited coating and the cover coating are deposited in a plasma consisting of 1-hexene as initial substance.
The oxidation process during the production of the TMDS coating proceeds slower than with pure oxygen and can be regulated in an especially sensitive manner if, according to another further development of the method, the oxygen is supplied as oxygen chemically bound in an alcohol for hardening the TMDS coating. This oxidation process by means of an alcohol can also be used for permeation blocking-coating systems which are deposited on a TMDS base. This type of oxidation is furthermore suited for all other oxidation processes of siloxanes in plasma. It is especially advantageous if the alcohol is methanol.